Fig. 4

Experimental results. The red and the blue circle are the local spectra of the original four qubit states. After applying local operations, the spectra are shown as the red and blue dots for |Ψ ⁽¹⁾〉 and |Ψ⁽²⁾〉, respectively. The data points in the cyan region do not meet the constraint (4). Error bars are obtained by Monte Carlo simulation (1000 runs)